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<html lang="en">
  <head>

    <meta charset="UTF-8" />

    <meta http-equiv="X-UA-Compatible" content="IE=edge" />

    <meta name="viewport" content="width=device-width, initial-scale=1.0" />

    <link rel="stylesheet" href="versions/3.3.7/iso_bootstrap3.3.7.css" />

    <link rel="stylesheet" href="versions/4.0.0/iso_bootstrap4.0.0.css" />

    <link rel="stylesheet" href="versions/5.0.2/iso_bootstrap5.0.2.css" />
    
    <title>Document</title>
  </head>
  
  <body>
    <div class="bootstrap3">
      <div class="custom-container">
        <div class="card">
          <input type="text" class="form-contol txt" placeholder="Bootstrap 3 Textbox" />
          <input type="button" class="btn btn-danger" value="Bootstrap 3 Button" />
        </div>
      </div>
    </div>

    <div class="bootstrap4">
      <div class="custom-container">
        <div class="card">
          <input type="text" class="form-contol txt" placeholder="Bootstrap 4 Textbox" />
          <input type="button" class="btn btn-danger" value="Bootstrap 4 Button" />
        </div>
      </div>
    </div>

    <div class="bootstrap5">
      <div class="custom-container">
        <div class="card">
          <input type="text" class="form-contol txt" placeholder="Bootstrap 5 Textbox" />
          <input type="button" class="btn btn-danger" value="Bootstrap 5 Button" />
        </div>
      </div>
    </div>

    <link rel="stylesheet" href="style.css" />
  </body>
</html>
